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Posts posted by Hartwig

  1. The signal ground here is always 0V. Sorry, I should have been posting a more dedicated schematic.

    How about this one? Maybe you need to play around a bit with the values of R1,3,5. But anyway this schematic shows the principle.

    If you built the circuit according to that schematic, you will have anice biased output at a DC offset level of roughly 2.5V. Also you are able to adjust the video level in a sensible range so you will end up with a signal level of 1Vpp when correctly terminated with 75ohms.

    If you want to use it as an output buffer stage, just add another 470uF Cap in series to Rout.

    The 75ohms Resistor on the very right hand side is actually the input of the next device. It works really nice for me. I'm using the LT1207, but you can choose one of your own flavour.

    Rin (75ohms) is there to terminate the previous stage which feeds its signal into this Buffer/Amp. In order to get multiple outputs from a sngle video source, just use Rin once, and connect the following circuits (all identical to this one) in parallel at this node, so the overall input impedance stays ~75ohms.


  2. :blink: Great! :)

    In case you consider to modify the circuit, or to add several outputs you might like to use a circuit like the one below. It's actually the default for a simple audio amp stage, but with a little changes, you get a nice video buffer stage with biased output and also variable amplification to adjust the video level.

    (Just remove C2, change R4 to 470ohm and replace R2 with a 1k var Resistor. Maybe play around with R1,3,5 by reducing their values, if needed)

    I'm using it in my DIY diversity receiver and it's perfect. Just take a Video-suitable

    Op-Amp (for example LT1207 or a MAXIM Video Op-Amp).


  3. Had a bad experience on a windy day, too. However, the wind was too strong to get back to the field, and my plane was about 1.3km away, still. So I tried to "gently" (while bumpy wind) prepare it's heading and behaviour, although gliding was out of the question. Then I could just watch it going down, trying to figure out where it will touch the ground.

    All of that was shortly before sunset, and the next 4 hours we weer searching for it in the dark and didn't find it anymore.

    So, the next day with the help of the video we found it.

    This was a real lecture to me! :unsure:

  4. Gil, it actually doesn't matter if it comes from Australia or Switzerland, as they're both outside european community. But if the value (marked outside on the packaging) is below 20$ for commercial, or below 40$ for a gift, there won't be any extra taxes.

    If it's above that, there will be, sometimes huge, taxes charged for it, as well as extra weeks of delay while the parcel sits inside customs offices, waiting to be processed.

  5. Thomas, I guess your RC TX is pretty good if you can still control your plane at a distance of 1500meters, or maybe my system is not optimal...

    I have a very nice video downlink, but I get so many glitches and 2 days ago I lost control of my plane and had a very bad crash because it didn't respond at all to any command anymore and it was at about 700m distance and ~120m Altitude, which still should be ok (unless someone used my channel...)

    Can you tell me which RC-system (TX and RX) did you use for that?



  6. Hi Mr.RC-CAM, thanks a lot for your efforts and results! Good to hear that at least something is similar to what I have on my systems, so there might be hope :-)

    I think you're right regarding the OSD. I did a few tests yesterday without the OSD and got better results. However, I will investigate more into this direction.

    Maybe reducing the video levels and low-pass-filtering the OSD's video signal might help, even though I get noise as well with the video coming from the camera.

    Do you maybe have some screenshots of the video signals displayed on an oscilloscope? I'd like to compare my systems to the systems you and the others on this forum are using. For me these measurements are really useful in troubleshooting and improving the quality.

    The test patterns I use are mainly Multiburst, white spike, white plane, Ramp and Color bars at 100% level.

    I'm very curious on Thomas' OSD. I think that the shade arund the letters will help to reduce the bandwidth also, thus reducing noise in the audio as well.

    Thanks a lot for any kind of help!! :rolleyes:



  7. Mark, I think that's right, they can drain a lot of power, but they can carry heavy loads, too.

    But the main thing in my opinion is the stability that they offer. There are about 60-70 developers working together on it, and they are very effective.

    I saw videos which prove incredible stability. You could just put the RC-Control aside, go to the toilet and return a few minutes after, and the QuadroCopter will still be in the same place and heigth where you left it, even in windy conditions. It's just amazing.

  8. -AT-Mr.RC-CAM: I tested with two 623s and a Comtech Receiver and got the noise on all of them, however it's better on the Comtech receiver.

    But I can reproduce it also with the Rangevideo TX 1000mW.

    I noticed that lots the lawmate sounds pretty popular and as I understand that you and Thomas are using them also. And you seem to be fine with them.

    Maybe it's related to temperature, that some part in the TX gets too hot and causes a drift where the receiver's PLL is overextended and can't handle it anymore?!

    But it's strange that on the Airwave receivers the noise just starts when a signal is fed into the audio input of the TX, and when I powercycle the TX the noise is gone again, despite the fact that the TX is still hot. And also the audio is nicely quite and fine when no video is fed into the TX.

    So I can reproduce the same behaviour with all of the TXs and RXs which I have.

    But since I don't believe too much in VooDoo :ph34r: , I will investigate more B)

    Did anyone of you happen to measure the video levels or check the TXs frequency stability over temperature? Unfortunately I don't have access to the required instruments.

  9. -AT-mieczotronix: I thought of something similar, and the problem is that this local sync generator must be exactly in sync with the original video signal, and keep free running when there's no signal to lock to, or even worse when the signal that comes in is total crud and might mess up the locking circuit.

    If these problems are overcome then this is a great solution.

    (Another option would be to sample the video signal and put it out again. So after the AD/DA conversion a new generated video signal is there, and stable. But would be again HUGE :-)

    Just my 2 cents,


  10. That program is called DGEarthTracker, you will find it here: www.dgadv.com

    It requires the VTG and GLL NMEA commands from the GPS receiver. On the EM-4xx receivers those seem to be disabled by default, so you have to enable them by sending the following strings to the EM4xx:

    $PSRF103,05,00,01,01*20 (enable VTG)

    $PSRF103,01,00,01,01*24 (enable GLL)

    And it works great! I got GoogleEarthPlus as well and I definitely prefer EarthTracker, because you can configure more parameters and it works seemless.

    However, it's shareware, but only $10 once. And it's definitely worth it.



  11. - Which Rx are you using during the shown scope example?

    =>The RXs are AWM623.

    - Are the audio outputs (with the recommended caps) terminated, or are they allowed to freely float? Does the noise go away with a 10K ohm loads on the R/L audio? How about 1K?

    => The audio output (R is used, L is not connected) is AC coupled (22uF) loaded with 10k. Loading with 1k doesn't help either :-(

    - Any chance the board layout of the Rx is allowing coupling between the video and audio? The pixel data is very fast rise time, so coupling can occur if the layout/wiring is not careful.

    => Each signal line is surrounded by ground.

    - Is the module's power sufficiently decoupled/bypassed? This includes the caps proximity to the module.

    => The TX has its own linear regulator, and the power line looks perfectly clean on the scope.

    I also notice that it doesn't start immediately when I power up the TX. For example when I touch the TX's audio input shortly, it starts. (see screenshot) When I short it to ground the distortion is still there.

    When I then power cycle the TX, it's gone.

    When I then touch the audio input, again the noise appears.

    Power cycling again, and the noise is gone.

    And so on...

    Any idea? :blink:


  12. I attached a screenshot of the video- and the audio waveform at the output of the receiver. The video input signal of the TX gets just a few letters from the OSD and black from the camera, and no signal is fed into the audio input of the TX.

    At the peaks in the video signal you can see spikes with a curve similar to a discharge of a capacitor after it.

    If I reduce the level of the video signal at the input of the TX, it doesn't affect the spikes in the audio.

    Does anyone have an idea what's happening?

    Does anyone experience similar effects?

    Any help is very much appreciated!




  13. What exactly do you mean with "information lost"?

    The module is onboard the plane, so that means as long as the plane and it's electronics are alive and the battery is full enough, the information gets burned into the video picture in realtime, and transmitted into the air.

    So as soon as you get close enough to the plane (aka video transmitter) to receive a usable signal, you will see the video with all the data information onscreen.

    Does this answer your question? Sorry if I misunderstood.



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